FIG. 1 shows a prior art TR switch 102 coupled to a low noise amplifier 104, analog front end functions 106 which include a local oscillator and mixer for mixing a signal modulated by a carrier in a frequency range such as 4.9 Ghz to 5.9 Ghz down to baseband for digitizing prior to processing as a succession of digital samples by baseband processor 110. The baseband processor 110 also generates a baseband transmit symbol stream, which is handled by analog front end functions 108 which include conversion to an analog signal by a DAC, mixing to a fixed modulation frequency such as in the range 4.9 Ghz to 5.9 Ghz, amplification by power amplifier 112, and coupling to the transmit port of a TR switch 102 for coupling to antenna 100.
In the operation of a wireless transceiver, different time intervals are used for transmission and reception, and the function of the TR switch 102 during transmit intervals is to couple maximum power from the power amplifier 112 to the antenna 100 and to prevent level transmit signals from damaging the low noise amplifier 104 input. During receive intervals, the function of the TR switch is to maximize coupling of low level signals from the antenna 100 port to the LNA 104, as any loss in this receive path prior to the LNA represents an undesired increase in the noise figure of the system.
In prior art systems, PIN diodes or GaAs MESFETS are used to provide the TR switch function. Previous attempts to use CMOS FETs in the Ghz range have suffered from performance shortcomings of a reduced 1 dB input compression point compared to the desired goal of 30 dBm, and an insertion loss which is in excess of 1 dB. Additionally, it has not been possible to combine external elements in a CMOS FET for which a wide range of frequency operation is available.
It is desired to have a transmit-receive switch which uses CMOS FETs, has two or more ranges of operation, and provides both low insertion loss and an improved 1 dB compression point. Additionally, it is desired to provide a transmit-receive switch which may be fabricated in CMOS triple well technology, thereby providing a single integrated circuit which includes baseband processing, front end signal processing for transmit and receive paths, and low noise amplifiers and power amplifiers which are coupled directly to the transmit-receive switch.